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Home Made Kiln Controller

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Bob Coyle    113

The k chip is cheap. I can't remember what the  other one S maybe. I think it uses platinum so it is real expensive. The K is good up to 1300C or around 2300 F.

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I seem to have been confused when looking at some specs, got an old thermocouple from a kiln that I can use. Good to know the chip will read up to there.

 

MAX31855 breakout board arrived and was wired up in about 5 minutes with the python libraries installed, example program working. Seemed so easy to read the thermocouple. Followed the tutorial on the Adafruit website.

 

Started looking into ways to log the temperature, got a bit lost in google drive trying to make their python libraries work so I could write the data to a google sheet. Never managed to get that working so I am writing out a .CVS format file with all the data in. It should log the temperature every minute. Makes a text file called Log with the date and time it is when you start the log.

import time
import sys
import os

import Adafruit_GPIO.SPI as SPI
import Adafruit_MAX31855.MAX31855 as MAX31855

TIME = time.strftime("%Y-%m-%d-%H:%M:%S")

CLK = 25
CS = 24
DO = 18
sensor = MAX31855.MAX31855(CLK, CS, DO)

firingHours = 8
firingMin = firingHours*60

file = open("Log" + TIME + ".txt", "a" )
file.write("Reading,Temperature,Internal Temperature\n")

for i in range (0,firingMin):
	file.write("%d,"%i + "%.2f" %sensor.readTempC() + ",%.2f" %sensor.readInternalC() + "\n")
	time.sleep(60)
file.close()

Ran a few tests putting it next to a fan heater and managed to get some workable stuff out. Now I just need some work to fire in the kiln so I can test out the temperature logging. Seemed like the simplest project to start with.

 

post-23281-0-37664800-1439382175_thumb.png

Edited by High Bridge Pottery

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Bob Coyle    113

Congrads !

 

looks like you got some temperature logged OK. I am not sure what you logged. the temperature on the left of the graph only goes up to 25. The graph shows a max of around 34???

 

Do you understand what the code is doing, or did you just copy it and run it?

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Yea it went to around 33-34degC when I put the thermocouple in front of the heater. I read quite a few tutorials about writing out text files. Could be a better way but this is what worked for me first. It seems simple to get the chip to work, just need sensor,readTempC() and spits out a reading. Will be good to test it on my kiln that has working thermocouple and controller to see how accurate it is.

 

Now I need to work out what to do with the temperature readings other than writing it to a file.  :unsure:  :mellow:

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Joseph F    867

Congrats your moving right along.

 

If I was you, the first thing I would do with the temperature readings is setup a fake kiln. Meaning that you want to record data increases to resemble your real kilns firing along side your fake kiln.

 

So say you fire 500/h to 2000F, just for arguments sake.

 

You would write something that records temp increase, and rate increases.

 

To do that you would setup some basic variables like:

 

currenttemp = # input from TC rasp pi

lasttemp = # input from TC rasp pi,write a small script that before currenttemp is overwrote, it saves the currenttemp integer information to this variable

rate = currenttemp - lasttemp  # this will give you the rate per how often you check this, so if you updated current temp every minute it would be rate per minute of change total. roughly. 

rateperhour = rate*60 #this would be rate times 60 rate checks, = 1 hour of rate checks, so if your increasing by 2F per minute, according to the last rate check, your current rate per hour would be, 120F/per hour.

 

setup a function that every hour, minute, or seconds even it records the rate, current temp, and rate per hour into an array. then you could look at that array and print out the results to see how accurate your TC is firing along with your other kiln's TC

 

just an idea of where i would go if I was at this point.

 

of course you could increase your effectiveness of everything by checking every second, then doing those maths. There is a lot of different things you could do, you could build segment variables, ramp variables etc. You could build an entire fake program, and run it along and have it fail if your TC doesn't work along with it and stuff. lots of fun things before you actually build a real control box and start pumping directions and volts into a kiln.

 

keep us updated@!

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Bob Coyle    113

I'll go along with Grype, It is good to have a the theoretical ramp graph to compare the run to. it gets a little more complicated if you are using a multi step ramp with holds.

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ggoodman    0

ever thought of using one of these? this guy built it for a reflow oven similar ramp soak step heating just diffrent temps.... from my research look like you can build difrent firing schedules then load them via the USB interface when you want to change the program.

 

 http://www.rocketscream.com/blog/product/ospid-kit/

 

this is the tree I am barking up.

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ggoodman    0

Ill be investigating a lot more in a couple weeks. Have  a friend who is a electricle engineer who writes a bunch of languages he thinks this could be a great option. as it is I am in my last three weeks of nursing school so that is occupying my time.

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curt    117

I think you already have the S chip, but I would suggest the R chip instead if you can get it.  R type is standard for use at Cone 10 temps and offers the best compromise for accuracy and durability among the various thermocouple types for a potters working at stoneware temps.

 

Most of the high-temperature gear I have seen on offer on EBay is K type, and a lot of the specs for different bits say they will go to 1300.  However, when you actually get the stuff in your hands you can tell it will not last any time at all at 1300, ie in continuous use at that temperature. 

 

However, I am rebuilding an old top loader (tomorrow or sometime later), but have already procured a couple of those cheap PID controllers ($30 to $50), some kanthal wire (elements) and some solid state relays (surprisingly/ridiculously cheap compared to what my local kiln co. wanted to do for me), so I am interested in how you go. 

 

I would be particularly interested in seeing this kind of basic homemade set up to control gas kiln solenoids and (icing on the cake) an oxyprobe or similar device to monitor and control reduction. 

 

Love your style/willingness to strike out on your own!

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This link was posted before but you might have missed it. Using one of these to control a gas kiln.

 

https://www.raspberrypi.org/blog/wifi-controlled-pottery-kiln/

 

The breakout I bought came with a type K and I have an old electric kiln type K that I am using. I haven't been doing too much on this recently as more important things but I am just about to convert my old electric to gas so hopefully needs must and I will sort out a little project on the pi.

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David Woodin    26

Omega.com in the USA has a 2 input data logger that allows you to download the information to your computer and view or print out a graph of your firing.  It is HH306A Thermometer/Data  Logger and comes with a disc to download what you need.

David

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RoriIltis    0

I am working on my project and also i spent quite a bit of time researching DIY controllers earlier this year after my kiln's controller died.

Once I was heading towards using an Arduino Uno with the MAX31855K chip, but I ended up just getting a PID ramp/soak controller from Auber Instruments. 

I didn't want to have deal with trouble-shooting any issues that might occur, and the Auber controller wasn't that much more expensive.

But programming a controller would have been fun.

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Tim T    46

Joel,

A couple of us down near Winchester have been talking about doing something similar - in my day job I do a lot of computer development, and currently have a project where we're using Arduinos (as they have more interfacing capabilities than the Pi). The thinking is:

- an Arduino for the sensors and a Pi or Intel board for the user interface

- better recording of temperature, voltage and current during the whole firing cycle

- prompts for manual tasks e.g. bungs in and out at set times or temperatures

- alarms for power cut, firing deviating too much from the plan, over firing or taking too long etc

- more intuitive and precise setting of the whole firing cycle, e.g. a modern consumer style user interface, and a controller that learns the max firing rate and the cooling rate of the kiln

- a touch screen for setting up the system and also showing what is hapening

- ability to log in remotely over WiFi or a wired network, so you can monitor things whilst ding other tasks

- for the gas kiln guys, eventually have servos controlling the gas flow and damper, plus interfacing to an oxygen meter

 

Unfortunately the day job is taking up too much time at the moment, and I need to get pots out for the Christmas shows etc, so the project is taking a back seat until the new year.

 

The day job project has International Paints/Akzo Nobel from Newcastle as one of its main partners, so I'll probably be going up your way in the coming year. We could meet for a beer and bounce some ideas around.

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Bob Coyle    113

Hi Tim

 

I have started to write an app in java for a kiln controller. I previously wrote one in VB 6 but it is now obsolete so I am starting over again. The app communicates with the arduino through the com port and receives temperature data and send control signals to turn a solid state switch on and off. It has some fail safe logic built in and allows multi ramp input.  I tried to send a zip file with the code, but It was not allowed. but if you are interested contact me directly and I will send it to you ( or anyone else who is interested)

 

Bob Coyle

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Joel,

A couple of us down near Winchester have been talking about doing something similar - in my day job I do a lot of computer development, and currently have a project where we're using Arduinos (as they have more interfacing capabilities than the Pi). The thinking is:

- an Arduino for the sensors and a Pi or Intel board for the user interface

- better recording of temperature, voltage and current during the whole firing cycle

- prompts for manual tasks e.g. bungs in and out at set times or temperatures

- alarms for power cut, firing deviating too much from the plan, over firing or taking too long etc

- more intuitive and precise setting of the whole firing cycle, e.g. a modern consumer style user interface, and a controller that learns the max firing rate and the cooling rate of the kiln

- a touch screen for setting up the system and also showing what is hapening

- ability to log in remotely over WiFi or a wired network, so you can monitor things whilst ding other tasks

- for the gas kiln guys, eventually have servos controlling the gas flow and damper, plus interfacing to an oxygen meter

 

Unfortunately the day job is taking up too much time at the moment, and I need to get pots out for the Christmas shows etc, so the project is taking a back seat until the new year.

 

The day job project has International Paints/Akzo Nobel from Newcastle as one of its main partners, so I'll probably be going up your way in the coming year. We could meet for a beer and bounce some ideas around.

 

Would be happy to meet up for a beer if you are ever in Newcastle. My project has taken a back seat too  :huh: had to reformat the Pi as it broke and I have no idea how to fix it. Probably be a bodge job for my gas kiln and then go from there.

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Well I know the thermocouple is completely out of wack. The kiln was reading 260c but my pi was reading 80c when I left. Not sure if I have the wrong kind of thermocouple in the chip. Nothing on the thermo that says its type. Looked at the theoretical voltage readings for thermocouples and being 3.5x lower doesn't make any sense, there isn't a type of thermocouple that would be reading that  :blink:

 

I am considering running to RSelectrical and buying a type N chip but who knows if that would work. If it is consistently off by 3.5x then I could brute force it and multiply my readings  ^_^ Will post the graph of the firing once I get in the studio.

 

Could be the wiring possibly....

 

Need a way to find out what thermocouple it is, might end up buying a new type K.

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PeterH    87

An observation rather than a theory.

 

Ratio between F & C is 9/5

(9/5)2 ~ 3.34

 

So if the conversion formula had used 5/9 rather than 9/5 ...

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I was using the sample program to show me the C and F reading while my other program logged the data in the background. Don't think there would be anything wrong with their example.

 

It is probably the thermocouple being the wrong type or the really old wire that I am using. Maybe I can figure out what kind it is on the old controller somewhere.

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So here is the data I collected. Top temperature was 330 even though it went up to 1260. Starting to think it could be a platinum thermocouple. Seemed to be 3.5 to 4x off the reading. 

 

Also dropped a lot of readings and gave me a value of 'nan' not sure what that means yet.

 

Need to find out what thermocouple this is and change the chip or spend the money on a type K.

Min along bottom and degC up.

gallery_23281_1039_5383.jpg

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PeterH    87
Also dropped a lot of readings and gave me a value of 'nan' not sure what that means yet.

 

NaN = Not a Number

https://en.wikipedia.org/wiki/NaN

 

It's basically a great way of handling those embarrassing situations such as an unanticipated divide by zero.

The NaN propagates through subsequent uses of the variable.

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Ok, after a little more research I think it is for sure spitting out nan because of the wrong type of thermocouple.

 

A type R thermocouple has 14mv~ at 1260c and would you have it a type K chip would read that as 330c. It has to be a platinum thermocouple and I am pretty sure now it is an R. Hopefully get the right chip and solder it instead of type K. Going to be £60 cheaper.

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